1. Field of the Invention
The present invention relates to an electric motor, in which a temperature sensing element for sensing the temperature of the motor coil is provided on a stationary part of the motor, such as the housing of the motor body, for the protection of the coil.
2. Description of the Related Art
The coil of an electric motor generates heat due to core loss and ohmic loss. Motors equipped with a coil heat protection function sense the temperature of the coil part to prevent coil heat loss resulting from heat generation. To sense the temperature of this coil, ordinarily the temperature sensing element is either embedded into the coil between the windings, or affixed to the coil using string.
FIGS. 7, 8A and 8B are schematics illustrating conventional methods for mounting a coil temperature sensing element to a motor. To graphically represent the coil part, FIG. 7 provides a cut-away view of one part of the motor. FIGS. 8A and 8B only show that part of the motor to which the temperature sensing element is mounted. The motor illustrated in FIG. 7 incorporates a stator 12, around which a coil 13 is wound, and a rotor 10, which is supported and rotated by a rotor shaft 11 inside the stator 12. At one axial end of the stator 12 there is a front flange 15, and at the other end there is a rear housing 14. A temperature sensing element 1 for sensing the temperature of the coil 13 of the stator 12 is a sensor such as a thermistor, the output from which is derived via a lead wire 3.
Conventionally, to mount a temperature sensing element 1 to a coil 13, the temperature sensing element 1 was inserted into the inside of the motor through an opening in the center of the rear housing 14 (indicated by an arrow in FIG. 7) to be either embedded between the exposed windings (FIG. 8A), or attached to the coil 13 with string (FIG. 8B).
FIG. 8A illustrates the method, whereby the temperature sensing element is embedded between the windings of a coil. To embed a temperature sensing element between the windings of a coil, when mounting the coil 13 to the stator 12 and subjecting the end of the coil to wire processing, a space is opened in the coil by spreading apart the windings, and after embedding and securing the temperature sensing element 1 in that space, impregnating is performed.
FIG. 8B illustrates the method, whereby a temperature sensing element is attached to a coil using a string. Even when the temperature sensing element is attached using this string, when mounting the coil 13 to the stator 12 and subjecting the end of the coil to wire processing, a string 40 is looped around a portion of the coil 13, and after securing the temperature sensing element 1 to the coil 13 with the string 40, impregnating is performed.
With the conventional methods of mounting a temperature sensing element to a coil, in order to form the space for inserting the temperature sensing element, or the space through which a string is passed, it is necessary to unwind the coil, which has been inserted are formed on the stator. Since this mounting operation is extremely time-consuming, it has been difficult to automate the task of mounting a temperature sensing element. And, in this mounting operation, there is a danger such that the coil will be damaged when the temperature sensing element is forced between the windings during the mounting operation.
Further, mounting methods that call for forcing a temperature sensing element between windings, or securing it with string pose problems in that the mounting location of the temperature sensing element is not fixed, and that temperature sensing precision varies because the measurement point in the motor where the temperture is sensed varies according to motors or the mount is not stable, so that the mounting attitude changes.